Catadioptric projection objective with pupil correction

ABSTRACT

A projection objective includes a plurality of optical elements configured so that, during use of the projection objective, radiation follows a path through the projection objective to image an object field in an object surface onto an image field in an image surface. The optical elements define a first group of refractive optical elements; a second group of optical elements downstream of the first group of refractive optical elements along the path, the second group of optical elements comprising a concave mirror; and a third group of refractive optical elements downstream of the second group of optical elements along the path. The projection objective has a first pupil surface along the path, and the projection objective comprises a Fourier lens group comprising a negative lens group arranged so that an absolute value of a Petzval radius at the first pupil surface is greater than 150 mm.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 12/511,515, filed Jul. 29, 2009, which is continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2007/001708, filed Feb. 28, 2007. The contents of these applications are hereby incorporated by reference in their entirety.

FIELD

The disclosure relates to a catadioptric projection objective including a plurality of optical elements arranged to image an off-axis object field arranged in an object surface of the projection objective onto an off-axis image field arranged in an image surface of the projection objective.

BACKGROUND

Catadioptric projection objectives are employed, for example, in projection exposure systems, in particular wafer scanners or wafer steppers, used for fabricating semiconductor devices and other types of microdevices and serve to project patterns on photomasks or reticles, hereinafter referred to generically as “masks” or “reticles,” onto an object having a photosensitive coating with ultrahigh resolution on a reduced scale.

SUMMARY

In some embodiments, the disclosure provides a catadioptric projection objective for microlithography suitable for use in the vacuum ultraviolet (VUV) range, where correction of imaging aberrations for different field points is facilitated. In certain embodiments, field dependent variations are largely avoided upon correction of imaging aberrations.

In some embodiments, the disclosure provides a catadioptric projection objective that includes a plurality of optical elements arranged to image an off-axis object field arranged in an object surface onto an off-axis image field arranged in an image surface of the projection objective. The optical elements form: a first, refractive objective part that can generate a first intermediate image from radiation coming from the object surface and including a first pupil surface; a second objective part including at least one concave mirror that can image the first intermediate image into a second intermediate image and including a second pupil surface optically conjugated to the first pupil surface; and a third objective part that can image the second intermediate image onto the image surface and including a third pupil surface optically conjugated to the first and second pupil surface. Optical elements arranged between the object surface and the first pupil surface form a Fourier lens group that includes a negative lens group arranged optically close to the first pupil surface.

The correction status of the first pupil surface can be influenced in a targeted manner to provide a first pupil surface having a surface curvature substantially weaker (radius of curvature substantially larger) than in certain known systems. A corrected pupil image is desirable to avoid field variations of correction effects induced by correcting elements positioned at the pupil position. Field curvature is generally the main aberration of the image of the entrance pupil to the first pupil surface. In order to correct the pupil image, a mechanism for correcting field curvature is desirably positioned in the objective part upstream the pupil surface.

A specific distribution of refractive power within the Fourier lens group can be provided to influence the pupil imaging which images the entrance pupil of the projection objective into the first pupil surface. Overall positive refractive power is involved for the Fourier lens group to collect radiation having a relatively large object-side numerical aperture into a beam passing through the first pupil surface. An undercorrection of the first pupil surface with regard to image curvature is thereby produced. Providing a negative lens group optically close to the first pupil surface may at least partly counteract the overall effect of the Fourier lens group on the curvature of the first pupil surface and provides a “flattening effect” on the curvature of the first pupil surface.

If it is often desired to effect a correction of aberrations essentially constant for all field points one or more correction elements may be placed in or optically close to a pupil surface. A variation of correcting effects across the field is also dependent on the path of ray bundles from different field points near the pupil surface. In case of large differences a correction element placed at or close to the pupil surface may have a field-dependent correcting effect. Even where a correction status of a pupil surface is relatively good, there is still a dependency from the angles of incidence of different rays at the pupil surface for different field points. It may be desirable to improve the correction status of the pupil surface. In particular, this can provide a mechanism to reduce the curvature of the first pupil surface.

Although it may be possible to provide at least one (weak) positive lens between the negative lens group and the pupil surface, the flattening effect may be improved where the negative lens group is arranged immediately upstream of the first pupil surface such that no positive lens is arranged between the negative lens group and the pupil surface.

Optionally, at least one negative lens of the negative lens group is arranged very close to or at the first pupil surface. Where negative refractive power is provided very close to or at the first pupil surface, the overall influence of this negative refractive power on the refractive power of the Fourier lens group is relatively small (due to a small value for the chief ray height, CRH), whereas at the same time the influence on correction of image field curvature of the pupil imaging may be relatively strong to provide the flattening effect on the curvature of the first pupil surface. In some embodiments, the negative lens group includes at least one negative lens arranged in a region where a marginal ray height MRH is substantially greater than a chief ray height CRH such that the condition |RHR|<0.2 is fulfilled for the ray height ratio RHR=CRH/MRH. Optionally, the condition |RHR|<0.1 holds.

In some embodiments, the negative lens group is formed by a single negative lens, whereby negative refractive power can be provided in an axially narrow space close to the first pupil surface. In certain embodiments, the negative lens group may be formed by two or more lenses including at least one negative lens, where the lenses in combination have negative refractive power.

In some embodiments, the negative lens group includes a biconcave negative lens immediately upstream of the first pupil surface, where the biconcave negative lens can be preceded by a positive lens upstream thereof such that the biconcave negative lens is the only lens of the negative lens group. A targeted concentration of negative refractive power close to the first pupil surface is thereby obtained.

In some embodiments, the Fourier lens group is configured such that a Petzval radius R_(P) at the first pupil surface obeys the condition |R_(P)|>150 mm, which is relatively large compared to certain known systems having comparable object-side numerical aperture. The Petzval radius as used here corresponds to the radius of curvature of the first pupil surface. The Petzval radius is proportional to the reciprocal of the Petzval sum 1/R_(P) of the Fourier lens group. The Petzval radius may be significantly larger than that, such as larger than 200 mm or larger than 250 mm.

In some embodiments, an aperture stop is positioned at the first pupil surface. The aperture stop may have a variable diameter allowing to adjust the utilized image-side numerical aperture NA. The variable aperture stop may be designed as a planar aperture stop, because little or no significant influence on telecentricity will generally occur when the diameter of the aperture stop is changed at a relatively flat first pupil surface.

In some embodiments the Fourier lens group has a first positive lens group (“P”) immediately following the object surface, a first negative lens group (“N”) immediately following the first positive lens group, a second positive lens group immediately following the first negative lens group, and a second negative lens group immediately following the second positive lens group and arranged optically close to the first pupil surface. Such Fourier lens group therefore includes two subsequent lens combinations of type P-N. A beneficial distribution of correcting effect for different aberrations, such as spherical aberration of the first pupil surface, astigmatism and field curvature may be obtained in this structure.

In some embodiments, the Fourier lens group has been improved with respect to lens material consumption and correcting effect by providing that the Fourier lens group includes at least one aspheric surface optically close to the object surface where RHR>|0.5| and at least one aspheric surface optically close to the first pupil surface where |RHR|<0.2. Optionally, at least one aspheric surface is provided in an intermediate region between the object surface and the first pupil surface in a region where the condition 0.2<|RHR|<|0.5| applies. The aspheric surface in the intermediate region may be provided in addition to the aspheric surfaces close to the field surface (object surface) and the first pupil surface.

In some embodiments, the third objective part is largely responsible for providing the high image-side numerical aperture provides significant contribution to correction of spherical aberration and coma of the imaging process. The third objective part, which can be purely refractive, may include between the third pupil surface and the image surface in his order: a front positive lens group; a zone lens having negative refractive power at least in a peripheral zone around an optical axis; and a rear positive lens group including a last optical element of the projection objective immediately upstream of the image surface.

The zone lens may have positive refractive power in a central zone around the optical axis. The zone lens may be designed as an aspheric lens configured to provide a negative refractive effect which increases from a central zone to a peripheral zone of the negative zone lens. In some embodiments, the zone lens is a meniscus lens having a concave surface facing the object surface. The zone lens may be arranged immediately upstream of the last optical element.

These features of the third lens group may be beneficial independent of the type of optical design and of the design of the first lens group in different projection objectives having a final imaging subsystem to image a final intermediate image onto the image surface.

Different types of projection objectives may be used. In some embodiments, the catadioptric projection objective is designed as an “in-line-system” i.e. as a catadioptric projection objective having one straight (unfolded) optical axis common to all optical elements of the projection objective. From an optical point of view, in-line systems may be favorable since optical problems caused by utilizing planer folding mirrors, such as polarization effects, can largely be avoided. Also from a manufacturing point of view, in-line systems may be designed such that conventional mounting techniques for optical elements can be utilized, thereby improving mechanical stability, of the projection objective.

In some embodiments, the second objective part has a mirror group having an object-side mirror group entry for receiving radiation coming from the object surface and an image-side mirror group exit for exiting radiation emerging from the mirror group exit towards the image surface, where the mirror group includes an even number of concave mirrors. In some embodiments, the second objective part has exactly two concave mirrors. The second objective part may be catadioptric (including at least one transparent lens in addition to at least one concave mirror) or catoptric (having only mirrors). In some embodiments capable of providing an obscuration free imaging without vignetting at very high image-side numerical apertures NA>1 all concave mirrors of the mirror group are optically remote from a pupil surface.

In certain embodiments, the second objective part has exactly one concave mirror positioned at or optically close to the pupil surface of the second objective part, and one or more negative lenses arranged ahead of the concave mirror in a region of relatively large marginal ray heights in order to correct axial chromatic aberration (CHL) and contribute to Petzval sum correction (“Schupmann principle”). The projection objective may include a first planar folding mirror (deflecting mirror) tilted relative to the optical axis to deflect radiation coming from the optical surface towards the concave mirror or to deflect radiation coming from the concave mirror towards the image surface. A second planar folding mirror optically downstream of the first planar folding mirror may be provided and oriented at right angles to the first folding mirror to allow parallel orientation of object surface and image surface. Representative examples of folded catadioptric projection objective using planar folding mirrors in combination with a single concave mirror are disclosed, for example, in US 2003/0234912 A1 or US 2004/0233405 A1 or WO 2005/111689 A2 or U.S. Pat. No. 6,995,833 B2. The disclosure of these documents related to the general layout of these systems is incorporated herein by reference.

The previous and other properties can be seen not only in the claims but also in the description and the drawings, wherein individual characteristics may be used either alone or in sub-combinations as embodiments of the disclosure and in other areas and may individually represent advantageous and patentable embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a meridional section of a projection objective;

FIG. 2 is a meridional section of a reference projection objective;

FIGS. 3A-3C show diagrams indicating the correction status of the first pupil surface of the reference system of FIG. 2;

FIGS. 4A-4C show diagrams indicating the correction status of the third pupil surface of the reference system shown in FIG. 2;

FIGS. 5A-5C show diagrams indicating the correction status of the first pupil surface in FIG. 1;

FIG. 6 shows a meridional section of a projection objective;

FIG. 7 shows an enlarged detail of the Fourier lens group LG1 of the projection objective in FIG. 6;

FIG. 8 shows a diagram representing the field variation of the RMS spot size of the projection objective in FIG. 6;

FIG. 9 shows a diagram indicating the field variation of tangential shell and sagittal shell in the embodiment of FIG. 6;

FIG. 10 shows a diagram of the dependency of the ray deflection angle RDA from the normalized pupil height PH for a zone lens L3-11 in FIG. 6;

FIG. 11 shows a meridional section of another embodiment of a catadioptric projection objective;

FIG. 12 shows an enlarged detail of the Fourier lens group LG1 of FIG. 11;

FIG. 13 shows a diagram representing the field variation of the RMS spot size of the projection objective in FIG. 11;

FIG. 14 shows a diagram indicating the field variation of tangential shell and sagittal shell in the embodiment of FIG. 11;

FIG. 15 shows a meridional section of another projection objective having a single concave mirror at a pupil surface;

FIG. 16 shows an enlarged detail of the Fourier lens group of FIG. 15;

FIG. 17 shows a diagram representing the field variation of the RMS spot size of the projection objective in FIG. 15;

FIG. 18 shows a diagram indicating the field variation of tangential shell and sagittal shell in the embodiment of FIG. 15.

FIG. 19 shows a partial view of the catadioptric projection objective of FIG. 11 with an aperture stop positioned at a first pupil surface.

DETAILED DESCRIPTION

In the following description, the term “optical axis” refers to a straight line or a sequence of straight-line segments passing through the centers of curvature of the optical elements. The optical axis can be folded by folding mirrors (deflecting mirrors). In the case of the examples presented here, the object is a mask (reticle) bearing the pattern of a layer of an integrated circuit or some other pattern, for example, a grating pattern. The image of the object is projected onto a wafer serving as a substrate that is coated with a layer of photoresist, although other types of substrates, such as components of liquid-crystal displays or substrates for optical gratings, are also feasible.

Where tables are provided to disclose the specification of a design shown in a figure, the table or tables are designated by the same numbers as the respective figures. Corresponding features in the figures are designated with like or identical reference identifications to facilitate understanding. Where lenses are designated, an identification L3-2 denotes the second lens in the third objective part (when viewed in the light propagation direction).

FIG. 1 shows a catadioptric projection objective 100 designed for ca. λ=193 nm UV operating wavelength. It is designed to project an image of a pattern on a reticle arranged in the planar object surface OS (object plane) into the planar image surface IS (image plane) on a reduced scale, for example, 4:1, while creating exactly two real intermediate images IMI1, IMI2. The effective object field OF and image field IF are off-axis, i.e. entirely outside the optical axis AX. A first refractive objective part OP1 is designed for imaging the pattern in the object surface into the first intermediate image IMI1 at an enlarged scale. A second, catoptric (purely reflective) objective part OP2 images the first intermediate image IMI1 into the second intermediate image IMI2 at a magnification close to 1:1. A third, refractive objective part OP3 images the second intermediate image IMI2 onto the image surface IS with a strong reduction ratio.

The path of the chief ray CR of an outer field point of the off-axis object field OF is drawn bold in FIG. 1 in order to facilitate following the beam path of the projection beam. For the purpose of this application, the term “chief ray” (also known as principal ray) denotes a ray running from an outermost field point (farthest away from the optical axis) of the effectively used object field OF to the center of the entrance pupil. Due to the rotational symmetry of the system the chief ray may be chosen from an equivalent field point in the meridional plane as shown in the figures for demonstration purposes. In projection objectives being essentially telecentric on the object side, the chief ray emanates from the object surface parallel or at a very small angle with respect to the optical axis. The imaging process is further characterized by the trajectory of marginal rays. A “marginal ray” as used herein is a ray running from an axial object field point (field point on the optical axis) to the edge of an aperture stop. That marginal ray may not contribute to image formation due to vignetting when an off-axis effective object field is used. The chief ray and marginal ray are chosen to characterize optical properties of the projection objectives. The radial distances between such selected rays and the optical axis at a given axial position are denoted as “chief ray height” (CRH) and “marginal ray height” (MRH), respectively.

Three mutually conjugated pupil surfaces P1, P2 and P3 are formed at positions where the chief ray CR intersects the optical axis. A first pupil surface P1 is formed in the first objective part between object surface and first intermediate image, a second pupil surface P2 is formed in the second objective part between first and second intermediate image, and a third pupil surface P3 is formed in the third objective part between second intermediate image and the image surface IS.

The second objective part OP2 includes a first concave mirror CM1 having the concave mirror surface facing the object side, and a second concave mirror CM2 having the concave mirror surface facing the image side. The mirror surfaces are both continuous or unbroken, i.e. they do not have a hole or bore in the area used for reflection. The mirror surfaces facing each other define a catadioptric cavity, which is also denoted intermirror space, enclosed by the curved surfaces defined by the concave mirrors. The intermediate images IMI1, IMI2 are both situated inside the catadioptric cavity well apart from the mirror surfaces.

Objective 100 is rotational symmetric and has one straight optical axis AX common to all refractive and reflective optical components (“In-line system”). There are no folding mirrors. An even number of reflections occurs. Object surface and image surface are parallel. There is no image flip. The concave mirrors have small diameters allowing to bring them close together and rather close to the intermediate images lying in between. The concave mirrors are both constructed and illuminated as off-axis sections of axial symmetric surfaces. The light beam passes by the edges of the concave mirrors facing the optical axis without vignetting. Both concave mirrors are positioned optically remote from a pupil surface rather close to the next intermediate image. The objective has an unobscured circular pupil centered around the optical axis thus allowing use as projection objectives for microlithography.

The projection objective 100 is designed as an immersion objective for λ=193 nm having an image side numerical aperture NA=1.55 when used in conjunction with a high index immersion fluid between the exit surface of the objective and the image surface. The projection objective is designed for a rectangular 26 mm*5.5 mm image field and is corrected for a design object field having object field radius (object height) 63.7 mm.

The specification for this design is summarized in Table 1. The leftmost column lists the number of the refractive, reflective, or otherwise designated surface, the second column lists the radius, r, of curvature of that surface [mm], the third column indicates aspheric surfaces “AS”. The fourth column lists the distance, d [mm], between a surface and the next surface, a parameter that is referred to as the “thickness” of the optical element, the fifth column lists the material employed for fabricating that optical element, and the sixth column lists the refractive index of the material employed for its fabrication. The seventh column lists the optically utilizable, clear, semi diameter [mm] (optically free radius) of the optical component. A radius of curvature r=0 in a table designates a planar surface (having infinite radius).

A number of surfaces (indicated AS) are aspherical surfaces. Table 1A lists the associated data for those aspherical surfaces, from which the sagitta or rising height p(h) of their surface figures as a function of the height h may be computed employing the following equation:

p(h)=[((1/r)h ²)/(1+SQRT(1−(1+K)(1/r)² h ²))]+C1·h ⁴ +C2·h ⁶+ . . . ,

where the reciprocal value (1/r) of the radius is the curvature of the surface in question at the surface vertex and h is the distance of a point thereon from the optical axis. The sagitta or rising height p(h) thus represents the distance of that point from the vertex of the surface in question, measured along the z-direction, i.e., along the optical axis. The constants K, C1, C2, etc., are listed in Table 1A.

First objective part OP1 imaging the (rectangular) effective object field OF into the first intermediate image IMI1 may be subdivided into a first lens group LG1 with overall positive refractive power between object surface and first pupil surface P1, and a second lens group LG2 with overall positive refractive power between first pupil surface P1 and the first intermediate image IMI1. First lens group LG1 is designed to image the telecentric entrance pupil of the projection objective into first pupil surface P1, thereby acting in the manner of a Fourier lens group performing a single Fourier transformation.

The first lens group includes, in this order from the object surface, an positive meniscus lens L1-1 with object-side convex aspheric surface, a positive meniscus lens L1-2 with object-side concave aspheric surface, a thick positive meniscus lens L1-3 with image-side concave aspheric surface and a biconcave negative lens L1-4 aspheric on the exit surface immediately upstream of the first pupil surface.

Negative lens L1-4 forms a negative lens group positioned optically close to the first pupil surface P1 at a position where the condition RHR<0.2 applies for the ray height ratio RHR=CRH/MRH.

A transparent plane parallel plate PP may optionally be positioned close to the first pupil surface P1. The plane parallel plate PP may be provided with one or two aspheric surfaces to act as a correcting element. Due to the position close to the pupil surface, any correcting effect of the parallel plate PP has essentially the same influence on all ray bundles originating from different field points such that little or no field variation of the correcting effect is obtained (essentially field-constant correcting effect).

The correcting element can be mounted in such a way it can be exchanged without removing the objective from the projection exposure system, and can be replaced by another correcting element, having another shape adapted to correct aberrations. Alternatively, or in addition, the correcting element may be configured to be moved or tilted relative to the nearest pupil position or other lenses in the optical system, enhancing the correction capabilities.

The second lens group LG2 includes a positive meniscus lens L1-5 with aspheric convex exit surface immediately downstream of the first pupil surface, a thin positive meniscus lens L1-6 with image-side concave surface, and a thin positive meniscus lens L1-7 having an object-side concave surface and an aspheric exit surface lens immediately upstream of the first intermediate image.

The negative lens group, which is formed by a single biconcave negative lens L1-4 in this embodiment, is effective to counteract the effect on image field curvature provided by the positive lenses L1-1 to L1-3 upstream thereof, thereby flattening the first pupil surface P1 while, at the same time, contributing only little to the overall refractive power of the Fourier lens group LG1. Therefore, the pupil surface can be flattened without necessitating additional positive refractive power in the Fourier lens group to counteract the negative power of the negative lens. This may be understood by considering a system of thin lenses (representing the Fourier lens group LG1). The overall refractive power of this system may be described by:

φ=Σω_(i)φ_(i)

where φ is the overall refractive power, φ_(i) is the refractive power of single lens with index i, and ω_(i) is the ratio MRH_(i)/MRH₁, where MRH_(i) is the marginal ray height at lens i and MRH₁ is the marginal ray height at the first pupil surface.

The image field curvature may be described by the Petzval sum:

PTZ=Σφ _(i) /n _(i)=0

where a value PTZ=0 represents an entirely flat (planar) surface.

According to these conditions the negative refractive power in a system desirably compensates the positive refractive power in order to correct for image field curvature. Obtaining a positive overall refractive power of the system involves a marginal ray height MRH, at the position of a negative lens or negative lenses that is smaller than the respective values at positive lenses. According to these conditions negative lenses at small marginal ray heights will typically compensate for image curvature effected by positive refractive power at larger marginal ray heights. The typical “belly-waist” structure of refractive projection objectives is a typical consequence following from these conditions. A negative lens group arranged close to an object surface or an image surface of an imaging system may be used to reduce image field curvature. Now consider the pupil imaging e.g. imaging the entrance pupil of the projection objective into the first pupil surface. In this pupil imaging the object (entrance pupil) is typically not accessible in telecentric systems since it is located almost at infinity. However, the image of the entrance pupil in the pupil imaging is the first pupil surface arranged in the optical system where the chief ray intersects the optical axis. Providing a negative lens group upstream of and close to that first pupil surface may be used to reduce the field curvature of the pupil imaging, i.e. may be used to flatten the first pupil surface.

Some beneficial effects of a negative lens group provided within the Fourier lens group optically close to the first pupil surface are now explained by comparing some relevant properties of the first embodiment shown in FIG. 1 with corresponding properties of a reference system REF shown in FIG. 2, where the reference system does not have the negative lens group. In the reference system REF, features and feature groups corresponding to respective features and feature groups of the embodiment of FIG. 1 are designated with the same reference identifications. Specifications of reference system REF are given in tables 2, 2A.

In order to illustrate the correction status of the projection objectives at various positions within the projection objective, use will be made of “field curve diagrams” and “spot diagrams”. A field curve diagram is a diagram displaying the distance between the paraxial tangential image position or the paraxial sagittal image position and the image plane for each field height. A spot diagram is a diagram displaying the intersection points with the image plane of a bundle of rays emerging from a field point. In the spot diagrams, the geometrical RMS R size is given by the following equation:

RMS R=SQRT(ΣR ² _(i))/k=SQRT(Σ(X _(i) −X ₀)²+(Y _(i) −Y ₀)²)/k

where Xi, Yi are the x and y coordinates of ray i at the image plane, k is the number of rays and X0, Y0 is the average position of the ray coordinates in the image surface.

The correction status of the first pupil surface P1 of the reference system REF in FIG. 2 is shown using spot diagrams in FIG. 3A and FIG. 3B and field curves in FIG. 3C. A significant image-field curvature is evident. The correction status of the third pupil surface P3 (within the third objective part OP3) is shown using spot diagrams (FIGS. 4A, 4B) and a field curve diagram (FIG. 4C). The diagrams of FIGS. 4A-4C indicate a significant degree of astigmatism. A large difference between the correction status of the first pupil P1 and the third pupil P3 is also evident from a comparison of these figures.

The Petzval radius R_(P) of the first lens group LG1 (Fourier lens group) performing the imaging of the entrance pupil onto the first pupil surface P1 is R_(P)=−139 mm. The image field curvature of the imaging of the third pupil is substantially overcorrected having a Petzval radius R_(P)=+110 mm. The last positive lens group between the third pupil P3 and the image surface IS is mainly responsible to provide the required image-side numerical aperture NA. Therefore, this lens group has strong positive refractive power. In the reference system, the image field curvature contribution provided by this lens group is difficult to compensate. A correction compromise is obtained by flattening the tangential shell, as evident from FIG. 4C.

In the following, third order aberrations refer to aberrations of the pupil image. The object of pupil imagery is the entrance pupil, which is assumed to be at infinity in object space.

The third order aberrations, represented by the Seidel aberration error sums SA3 (third order spherical aberration), CMA3 (third order coma), AST3 (third order astigmatism), PTZ3 (third order Petzval sum) and DIS3 (third order distortion) are as follows:

SA3=−3.279689 mm, CMA3=−0.693865 mm, AST3=−0.811623 mm, PTZ3=−5.011397 mm and DIS3=−6.331224 mm.

Significant improvements are obtained in the embodiment of FIG. 1, which includes negative lens group L1-4 immediately upstream of the first pupil surface. The correction status of the first pupil surface P1 is given in the spot diagrams in FIG. 5A and FIG. 5B and the field curves in FIG. 5C. The Seidel aberration sums are as follows:

SA3=1.087472, CMA3=0.083425, AST3=1.342253, PTZ3=−2.642283 and DIS3=−2.242963.

It is evident that the spot size is significantly smaller than in the reference system (Note that scales differ by factor 10 between FIGS. 3A, 3B and FIGS. 5A, 5B). Further, the correction of tangential and sagittal shell is substantially improved (scales differ by factor 20 between FIGS. 3C and 5C). These data indicate a significantly improved correction status. The Petzval radius R_(P) of the first pupil surface is R_(P)=−290 mm, which is a significant improvement when compared to the reference system (R_(P)=−139 mm)

FIG. 6 shows a catadioptric projection objective 600 designed as an immersion objective for λ=248 nm having an image-side numerical aperture NA=1.47 when used in conjunction with a high index immersion fluid between the exit surface of the objective and the image surface. The projection objective is designed for a rectangular 26 mm×5.5 mm image field. At NA=1.47 a maximum ray angle in the immersion liquid is 72.65°, the ray angle being measured between the propagation direction of the ray having maximum inclination towards the optical axis, and the optical axis.

The sequence of objective parts and lens groups is the same as in FIG. 1, indicated by using the same reference identifications. The first lens group LG1 performing the Fourier transformation between the object surface OS and the first pupil surface P1 is shown in detail in FIG. 7. The specifications are given in Tables 6, 6A.

The first lens group LG1 includes, in this sequence from the object surface OS to the first pupil surface P1, a biconvex positive lens L1-1 having a strongly curved entry surface and an almost flat exit surface, a negative meniscus lens L1-2 having a concave entry surface facing the object surface, a biconvex positive lens L1-3, a thin positive lens L1-4 having a strongly aspheric exit surface providing positive refractive power around the optical axis and negative refractive power in a zone near the outer edge of the lens, and a negative group formed by a single biconcave negative lens L1-5 immediately upstream and very close to the first pupil surface P1. The structure of this lens group includes two lens combinations of type P-N, where P represents positive refractive power and N represents negative refractive power. The first lens combination P-N formed by lenses L1-1 and L1-2 provides a strong contribution to correction of spherical aberration of the pupil (PSA). Negative lens L1-5 contributes to correction of third order spherical aberration of the pupil (PSA3) and coma (CMA3). The second P-N combination formed by positive lenses L1-3 and L1-4 and negative lens L1-5 secures correction of astigmatism (AST3) and image field curvature (PTZ3). The contributions of the single lenses to third order Seidel aberrations are summarized in Table A.

TABLE A Lens SA3 CMA3 AST3 PTZ3 L1-1 0.525336 −0.325503 −2.799435 −1.937709 L1-2 1.798902 −0.285417 0.416959 0.062927 L1-3 −1.755569 0.247167 1.457322 −2.126689 L1-4 −1.05019 −1.015048 0.872844 −1.165997 L1-5 0.907359 1.122079 0.492766 2.768379

It is evident that the imaging of the entrance pupil onto the first pupil surface P1 has a good correction status. This is also evident from FIG. 8 showing a diagram of the variation of the RMS spot size (in mm) as a function of the fractional object height FBY in the first pupil surface. The best focal plane is at −0.346 mm from the specified pupil position. This plane provides a preferred position for a correcting element, such as an aspheric plane parallel plate PP as discussed in connection with FIG. 1. The diagram of FIG. 9 shows that the field variation of tangential shell and sagittal shell is significantly improved (i.e. reduced) when compared to the reference system REF. The first pupil surface has only slight curvature, represented by a Petzval radius R_(P)=−291 mm.

In the embodiment of FIG. 6, the third objective part provides a significant contribution to correction of spherical aberration and coma of the object imaging (the imaging between the object surface OS and the image surface IS optically conjugated thereto). The third objective part includes, between the third pupil surface P3 and the image surface IS, in this order a biconvex positive lens L3-10 serving as a positive front lens, a zone lens L3-11 having negative refractive power in a peripheral zone apart the optical axis and positive refractive power in a center region including the optical axis, and a plano-convex lens L3-12 forming a rear positive lens group immediately upstream of the image surface. The zone lens L3-11 has a rotatainally symmetric aspheric exit surface. In order to demonstrate the optical effect of zone lens L3-11 the diagram in FIG. 10 shows a ray deflection angle RDA (in degree) on the abscissa and the normalized pupil height PH on the ordinate. The ray deflection is demonstrated for a ray bundle originating from the optical axis. It is evident that the sense of deflection changes sign between the middle region around the optical axis (PH=0) and the edge of the pupil (PH=1) at about PH=0.95. This lens has a strong correcting effect on spherical aberration and coma of the object imaging.

A further embodiment having the general layout as shown in FIG. 1 or 6 is shown in FIG. 11. The specifications are given in Table 11, 11A. The immersion-type projection objective 1100 is designed for operation wavelength λ=193 nm and has an image-side NA=1.43 in a rectangular field of size 26 mm×4 mm. All lenses are made from the same material, fused silica (SiO₂). The structure of the first lens group LG1 (Fourier lens group) is shown in detail in FIG. 12. The first group includes only four lenses, namely a biconvex positive lens L1-1, a biconvex positive lens L1-2, a positive meniscus lens L1-3 having an image-side concave surface, and a biconcave negative lens L1-4 forming the negative lens group immediately upstream of the first pupil surface P1. Aspheric surfaces, marked by “X” are used to support correction of field-dependent and aperture-dependent aberrations. The aspheric surface on the entry-side of first lens L1-1 immediately following the object surface contributes particularly to correction of the field-dependent aberrations, such as distortion. The aspheric surface on the exit-side of negative lens L1-4 immediately upstream of the pupil surface is predominantly effective to correct pupil aberrations essentially without influencing field-dependent aberrations. An intermediate asphere on the exit-side of biconvex lens L1-2 influences both field-dependent and aperture-dependent aberrations.

The correction status of first pupil surface P1 is represented by the diagrams in FIG. 13, showing the variation of the spot RMS across the field, and the tangential and sagittal shells are given in FIG. 14.

A further embodiment of a catadioptric projection objective 1500 designed for X=193 nm UV operating wavelength is shown in FIG. 15. An image-side numerical aperture NA=1.5 is obtained in a rectangular 26 mm×5 mm image field when used in immersion-operation with an immersion fluid between the exit surface of the projection objective and the image surface. The specification is given in Tables 15, 15A.

Folded projection objective 1500 is designed to project an image of a pattern on a reticle arranged in the planar object surface OS (object plane) into the planar image surface IS (image plane) on a reduced scale, for example, 4:1, while creating exactly two real intermediate images IMI1, IMI2. The rectangular effective object field OF and image field IF are off-axis, i.e. entirely outside the optical axis AX. A first refractive objective part OP1 is designed for imaging the pattern in the object surface into the first intermediate image IMI1. A second, catadioptric (refractive/reflective) objective part OP2 images the first intermediate image IMI1 into the second intermediate image IMI2 at a magnification close to 1:(−1). A third, refractive objective part OP3 images the second intermediate image IMI2 onto the image surface IS with a strong reduction ratio.

Three mutually conjugated pupil surfaces P1, P2 and P3 are formed at positions where the chief ray CR intersects the optical axis. A first pupil surface P1 is formed in the first objective part between object surface and first intermediate image, a second pupil surface P2 is formed in the second objective part between first and second intermediate image, and a third pupil surface P3 is formed in the third objective part between second intermediate image and the image surface IS.

The second objective part OP2 includes a single concave mirror CM. A first planar folding mirror FM1 is arranged optically close to the first intermediate image IMI1 at an angle of 45° to the optical axis AX such that it reflects the radiation coming from the object surface in the direction of the concave mirror CM. A second folding mirror FM2, having a planar mirror surface aligned at right angles to the planar mirror surface of the first folding mirror, reflects the radiation coming from the concave mirror CM in the direction of the image surface, which is parallel to the object surface.

The folding mirrors FM1, FM2 are each located in the optical vicinity of an intermediate image, so that the etendue (geometrical flux) is kept small. The intermediate images are optionally not located on the planar mirror surfaces, which results in a finite minimum distance between the intermediate image and the optically closest mirror surface. This is to ensure that any faults in the mirror surface, such as scratches or impurities, are not imaged sharply onto the image surface.

The first objective part OP1 includes two lens groups LG1, LG2 each with positive refractive power on either side of the first pupil surface P1. First lens group LG1 is designed to image the telecentric entrance pupil of the projection objective into the first pupil surface P1, thereby acting in the manner of a Fourier lens group performing a single Fourier transformation.

FIG. 16 shows an enlarged detail of the first lens group LG1 (Fourier lens group) imaging the object surface onto the first pupil surface P1. The first lens group includes a plane parallel plate PP adjacent to the object surface, a thin positive meniscus lens L1-1, a thick positive meniscus lens L1-2, a thin, strongly aspheric meniscus lens L1-3 having an aspheric image-side concave surface, a thick, positive meniscus lens L1-4 and a negative group formed by a single biconcave negative lens L1-5 immediately upstream of the first pupil surface P1 and optically close thereto. The positive meniscus lenses concave towards the pupil surface have strong positive power providing a strongly converging effect on the ray bundles, but there is only little contribution to image-field curvature due to the similar radii of the entrance and exit surfaces.

The correction status of first pupil surface P1 is represented by the diagrams in FIG. 17, showing the variation of the spot RMS across the field, and the tangential and sagittal shells are given in FIG. 18.

FIG. 19 shows a partial view of the catadioptric projection objective of FIG. 11 with an aperture stop AP positioned at a first pupil surface.

The above description of embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present disclosure and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. It is sought, therefore, to cover all changes and modifications as fall within the spirit and scope of the disclosure, as defined by the appended claims, and equivalents thereof.

TABLE 1 NA = 1.55; field size 26 mm * 5.5 mm; λ = 193 nm Surface Radius Thickness Material Index (193 nm) ½ Diameter  0 0.000000 29.999023 AIR 1.00000000 63.700  1 0.000000 −0.293904 AIR 1.00000000 76.311  2 116.967388 AS 33.971623 SIO2V 1.56078570 93.710  3 268.858710 45.405733 AIR 1.00000000 92.342  4 −252.724978 AS 58.607153 SIO2V 1.56078570 92.157  5 −152.905212 0.986967 AIR 1.00000000 102.264  6 100.588881 94.936165 SIO2V 1.56078570 89.748  7 480.541211 AS 22.683526 AIR 1.00000000 61.038  8 −151.461922 9.967307 SIO2V 1.56078570 58.676  9 −1104.178549 AS 2.998283 AIR 1.00000000 54.598 10 0.000000 0.000000 AIR 1.00000000 53.972 11 0.000000 26.000000 AIR 1.00000000 53.972 12 −4615.634680 9.983258 SIO2V 1.56078570 77.043 13 −7648.187834 9.234701 AIR 1.00000000 82.010 14 −625.750713 48.866298 SIO2V 1.56078570 85.509 15 −110.073136 AS 47.938753 AIR 1.00000000 90.434 16 693.459276 15.566986 SIO2V 1.56078570 114.997 17 2225.036283 111.995402 AIR 1.00000000 115.765 18 −209.012550 24.611839 SIO2V 1.56078570 126.681 19 −181.333947 AS 37.469604 AIR 1.00000000 129.924 20 0.000000 238.315935 AIR 1.00000000 129.948 21 −214.798316 AS — REFL 1.00000000 151.231 22 186.831531 AS 238.315935 REFL 1.00000000 153.712 23 0.000000 37.462671 AIR 1.00000000 111.274 24 297.174670 29.574318 SIO2V 1.56078570 123.808 25 1191.420870 35.484494 AIR 1.00000000 123.384 26 4081.914442 22.323161 SIO2V 1.56078570 122.901 27 273.503277 AS 0.998916 AIR 1.00000000 122.715 28 231.074591 AS 9.994721 SIO2V 1.56078570 108.656 29 162.434674 7.329878 AIR 1.00000000 100.728 30 173.924185 9.996236 SIO2V 1.56078570 100.278 31 147.324038 39.865421 AIR 1.00000000 96.038 32 517.833939 AS 9.994259 SIO2V 1.56078570 95.918 33 418.975568 18.691694 AIR 1.00000000 97.853 34 402.609022 9.991838 SIO2V 1.56078570 103.816 35 225.169608 AS 18.474719 AIR 1.00000000 105.756 36 350.705440 AS 25.452147 SIO2V 1.56078570 107.818 37 −3388.791523 12.488356 AIR 1.00000000 110.250 38 1008.270218 AS 41.022442 SIO2V 1.56078570 119.521 39 −314.632041 3.943706 AIR 1.00000000 121.832 40 1442.963243 AS 12.476333 SIO2V 1.56078570 126.022 41 −1002.829857 14.096377 AIR 1.00000000 126.891 42 194.591039 81.128704 SIO2V 1.56078570 132.890 43 −264.895277 AS −22.880987 AIR 1.00000000 131.108 44 0.000000 −0.362185 AIR 1.00000000 132.343 45 0.000000 24.001275 AIR 1.00000000 132.533 46 159.644367 50.327970 SIO2V 1.56078570 109.736 47 494.742901 AS 0.961215 AIR 1.00000000 105.155 48 328.066727 14.868291 SIO2V 1.56078570 92.427 49 −3072.231603 AS 0.927658 AIR 1.00000000 86.384 50 84.317525 69.022697 LuAG 2.15000000 64.842 51 0.000000 3.100000 HINDLIQ 1.65002317 24.540 52 0.000000 0.000000 15.928

TABLE 1A Aspheric constants SRF 2 4 7 9 15 K 0 0 0 0 0 C1 −4.353148e−08 −9.800573e−08 2.666231e−07 1.295769e−07 1.774606e−08 C2 −1.948518e−13 5.499401e−13 −1.471516e−11 1.032347e−11 1.042043e−13 C3 −3.477204e−16 −1.499103e−16 −1.385474e−15 5.718200e−15 2.794961e−17 C4 2.346643e−20 −1.967686e−20 2.138176e−18 −4.988183e−18 −3.892158e−21 C5 −2.078112e−24 4.517642e−24 −1.482225e−22 1.949505e−21 4.464755e−25 C6 −8.347999e−31 −2.738209e−28 −8.304062e−27 −2.335999e−25 4.773462e−30 C7 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 19 21 22 27 28 K 0 −2.01691 −1.35588 0 0 C1 −1.294881e−08 −1.791441e−08 1.799581e−08 −2.305522e−07 −5.364751e−08 C2 2.960445e−14 1.393731e−13 6.604119e−14 −2.977863e−12 2.985313e−12 C3 −3.744673e−18 −1.959652e−18 1.091967e−18 1.067601e−15 1.185542e−16 C4 3.872183e−22 3.972150e−23 3.177716e−23 −7.036742e−20 −5.029250e−20 C5 −1.724706e−26 −6.577183e−28 −5.281159e−28 2.314154e−24 3.896020e−24 C6 4.346424e−31 6.141114e−33 1.575655e−32 −3.151486e−29 −1.479810e−28 C7 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 32 35 36 38 40 K 0 0 0 0 0 C1 2.753990e−08 1.438723e−07 4.030346e−08 4.491651e−08 −9.637167e−08 C2 −2.426854e−11 −2.226044e−11 −6.610222e−12 −5.791619e−12 3.256893e−12 C3 1.360579e−15 1.482620e−15 2.501723e−16 5.024169e−16 −9.241857e−17 C4 −1.150640e−19 −5.040252e−20 −2.574681e−21 −3.768862e−20 9.112235e−21 C5 7.525459e−24 1.831772e−24 −7.619628e−25 1.711080e−24 9.519978e−26 C6 −2.203312e−30 −8.726413e−29 1.815817e−29 −3.990765e−29 −1.423818e−29 C7 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 43 47 49 K 0 0 0 C1 5.213696e−08 −1.687244e−07 1.276858e−07 C2 −2.852489e−13 1.277072e−11 1.143276e−12 C3 6.349974e−17 −5.376139e−16 −2.525252e−16 C4 −4.223029e−21 1.564911e−20 9.197266e−20 C5 1.155960e−25 −3.759137e−25 −8.401499e−24 C6 −1.415349e−30 1.266337e−29 6.171793e−28 C7 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00

TABLE 2 (REF): NA = 1.55; field size 26 mm * 5.5 mm; λ = 193 nm Surface Radius Thickness Material Index (193 nm) ½ Diameter  0 0.000000 29.999023 AIR 1.00000000 63.700  1 0.000000 −0.017795 AIR 1.00000000 76.344  2 171.343027 AS 42.631678 SIO2V 1.56078570 85.956  3 −4741.853546 61.874338 AIR 1.00000000 86.356  4 105.977997 65.572103 SIO2V 1.56078570 88.863  5 −861.150434 AS 6.951388 AIR 1.00000000 82.403  6 258.046433 33.648405 SIO2V 1.56078570 67.159  7 1920.848867 AS 8.790277 AIR 1.00000000 50.974  8 0.000000 0.000000 AIR 1.00000000 47.230  9 0.000000 26.000000 AIR 1.00000000 47.230 10 0.000000 10.337048 SIO2V 1.56078570 61.729 11 0.000000 48.824997 AIR 1.00000000 65.126 12 −409.968959 9.999996 SIO2V 1.56078570 87.149 13 −1728.574510 AS 0.999396 AIR 1.00000000 92.240 14 −1262.850901 37.699713 SIO2V 1.56078570 94.725 15 −164.338442 35.734593 AIR 1.00000000 97.786 16 −892.837978 27.787355 SIO2V 1.56078570 106.595 17 −216.768119 AS 37.495802 AIR 1.00000000 107.808 18 0.000000 231.516797 AIR 1.00000000 107.221 19 −184.700839 AS −231.516797 REFL 1.00000000 157.546 20 202.731693 AS 231.516797 REFL 1.00000000 156.228 21 0.000000 37.496341 AIR 1.00000000 114.709 22 162.462380 39.081598 SIO2V 1.56078570 112.418 23 264.446518 AS 63.339427 AIR 1.00000000 109.444 24 −571.769195 AS 9.999663 SIO2V 1.56078570 91.313 25 708.749519 17.121515 AIR 1.00000000 87.569 26 −507.008359 9.999717 SIO2V 1.56078570 86.854 27 140.591845 19.187442 AIR 1.00000000 84.837 28 184.194102 AS 15.968244 SIO2V 1.56078570 86.582 29 283.845514 31.748225 AIR 1.00000000 90.637 30 4904.309359 10.047458 SIO2V 1.56078570 103.627 31 274.252599 AS 13.944029 AIR 1.00000000 113.490 32 309.375419 AS 28.215577 SIO2V 1.56078570 120.624 33 −920.430769 1.767414 AIR 1.00000000 124.772 34 18975.064444 AS 70.355114 SIO2V 1.56078570 127.703 35 −162.879880 12.292563 AIR 1.00000000 132.134 36 −2025.460472 AS 9.999587 SIO2V 1.56078570 141.670 37 −722.326749 0.998787 AIR 1.00000000 143.067 38 276.303253 73.567109 SIO2V 1.56078570 150.848 39 −523.286381 AS −10.418710 AIR 1.00000000 149.454 40 0.000000 −0.362185 AIR 1.00000000 145.848 41 0.000000 11.777558 AIR 1.00000000 145.992 42 203.342152 65.192017 SIO2V 1.56078570 131.067 43 −779.130399 AS 0.997958 AIR 1.00000000 126.720 44 305.958782 21.191217 SIO2V 1.56078570 103.169 45 −48623.319668 AS 0.987133 AIR 1.00000000 97.187 46 95.078716 76.560136 LuAG 2.15000000 71.117 47 0.000000 3.100000 HINDLIQ 1.65002317 24.554 48 0.000000 0.000000 15.926

TABLE 2A Aspheric constants SRF 2 5 7 13 17 K 0 0 0 0 0 C1 5.535754e−09 −2.163453e−08 2.131940e−07 −6.511619e−08 1.346551e−08 C2 −2.217501e−12 3.505228e−13 2.096996e−11 2.291139e−13 7.406450e−13 C3 1.496293e−16 3.144204e−15 2.247871e−15 −8.522321e−17 2.478135e−17 C4 −8.752146e−21 −5.148203e−19 2.662065e−18 3.174503e−21 4.410963e−22 C5 2.789483e−25 3.453724e−23 −1.491642e−21 −1.364637e−25 1.313895e−26 C6 −2.329972e−30 −9.033416e−28 6.227531e−25 4.124720e−30 −8.547823e−31 C7 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 19 20 23 24 28 K −1.52592 −1.42277 0 0 0 C1 −1.765080e−08 1.613577e−08 −4.798352e−08 4.255285e−08 −1.477745e−07 C2 4.917900e−14 4.357122e−14 −1.311955e−12 −1.146206e−11 1.210948e−12 C3 −9.914290e−19 9.093916e−19 3.514210e−18 6.521380e−16 −5.978764e−16 C4 5.089307e−24 8.683689e−24 1.024784e−21 −6.959952e−20 5.086484e−20 C5 −1.439617e−28 −2.826288e−29 1.466905e−25 8.075085e−24 −2.048151e−24 C6 −2.489761e−34 3.718326e−33 −6.750818e−30 −3.306910e−28 1.559775e−28 C7 0.000000e+00 C8 0.000000e+00 C9 0.000000e+00 SRF 31 32 34 36 39 K 0 0 0 0 0 C1 −5.803167e−08 −8.321353e−08 −3.416619e−08 −3.711339e−08 4.221371e−09 C2 5.110289e−12 3.106108e−12 1.834441e−12 3.509157e−13 −1.476275e−13 C3 −7.215213e−16 −1.869923e−16 −1.168356e−16 1.204985e−17 3.254133e−18 C4 4.298822e−20 7.706750e−21 −1.174247e−22 6.896527e−22 9.967170e−22 C5 −1.225430e−24 −4.141276e−25 4.114824e−25 3.435906e−26 −5.090064e−26 C6 7.229558e−30 1.166645e−29 −1.539536e−29 −2.039666e−30 6.695129e−31 C7 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 43 45 K 0 0 C1 6.584837e−09 4.103097e−08 C2 1.476709e−12 1.320693e−12 C3 −2.128509e−16 2.055670e−16 C4 1.488828e−20 −1.513267e−20 C5 −5.015220e−25 8.328043e−25 C6 7.209855e−30 −7.654058e−30 C7 0.000000e+00 0.000000e+00 C8 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00

TABLE 6 NA = 1.47; field size 26 mm * 5.5 mm; λ = 248 nm Surface Radius Thickness Material Index (248 nm) ½ Diameter  0 0.000000 29.999023 AIR 1.00000000 63.700  1 0.000000 −0.016587 AIR 1.00000000 75.565  2 128.928301 AS 42.026693 SIO2V 1.50885281 87.914  3 −2130.241282 44.327573 AIR 1.00000000 87.576  4 −117.301124 AS 37.980898 SIO2V 1.50885281 87.249  5 −121.095557 0.999318 AIR 1.00000000 97.646  6 124.335144 49.904800 SIO2V 1.50885281 88.572  7 −1015.089235 0.999887 AIR 1.00000000 85.114  8 841.474542 19.999813 SIO2V 1.50885281 79.220  9 −265.863207 AS 24.244189 AIR 1.00000000 74.122 10 −130.163272 19.998818 SIO2V 1.50885281 61.644 11 245.744624 AS 8.799263 AIR 1.00000000 54.069 12 0.000000 0.000000 AIR 1.00000000 53.816 13 0.000000 0.998863 AIR 1.00000000 53.816 14 262.324322 24.657808 SIO2V 1.50885281 60.964 15 −241.892483 1.204928 AIR 1.00000000 64.095 16 −388.893369 20.002393 SIO2V 1.50885281 65.782 17 −134.956755 AS 95.737496 AIR 1.00000000 68.599 18 270.042558 21.031793 SIO2V 1.50885281 102.358 19 651.399601 64.989823 AIR 1.00000000 102.511 20 −126.975206 19.999827 SIO2V 1.50885281 102.966 21 −145.489260 AS 37.494736 AIR 1.00000000 110.060 22 0.000000 275.711491 AIR 1.00000000 116.538 23 −253.239170 AS — REFL 1.00000000 195.865 24 186.748589 AS 275.711491 REFL 1.00000000 140.517 25 0.000000 37.497070 AIR 1.00000000 114.897 26 −4183.753618 43.458815 SIO2V 1.50885281 118.592 27 −202.559737 AS 13.648419 AIR 1.00000000 119.292 28 −175.419986 AS 19.999522 SIO2V 1.50885281 116.494 29 −154.929816 0.999549 AIR 1.00000000 118.150 30 −229.271599 19.999486 SIO2V 1.50885281 105.369 31 122.750670 AS 49.793521 AIR 1.00000000 100.243 32 190.556325 AS 46.859904 SIO2V 1.50885281 121.109 33 −943.347591 7.041362 AIR 1.00000000 121.790 34 −845.190598 19.999826 SIO2V 1.50885281 122.081 35 147.937513 AS 29.168833 AIR 1.00000000 128.004 36 1388.526462 AS 45.306600 SIO2V 1.50885281 131.120 37 −523.436578 4.347825 AIR 1.00000000 133.458 38 5449.999826 AS 19.999851 SIO2V 1.50885281 134.608 39 −348.816325 0.999597 AIR 1.00000000 137.891 40 340.272237 AS 67.587519 SIO2V 1.50885281 153.819 41 −323.687667 58.231540 AIR 1.00000000 155.356 42 0.000000 0.000000 AIR 1.00000000 154.131 43 0.000000 −57.242893 AIR 1.00000000 154.131 44 225.119659 90.762438 SIO2V 1.50885281 154.660 45 −354.115170 AS 0.997569 AIR 1.00000000 152.747 46 332.230008 48.061330 SIO2V 1.50885281 131.162 47 −1361.523117 AS 1.268990 AIR 1.00000000 127.295 48 −810.795253 19.998161 SIO2V 1.50885281 122.580 49 −451.036733 AS 0.994751 AIR 1.00000000 113.480 50 93.456855 76.027617 LUAG 2.02093434 71.508 51 0.000000 3.100000 HIL001 1.54048002 26.023 52 0.000000 0.000000 15.926

TABLE 6A Aspheric constants SRF 2 4 9 11 17 K 0 0 0 0 0 C1 −4.384112e−08 −4.412855e−08 2.029683e−07 3.217532e−08 6.242700e−08 C2 6.119422e−13 −1.990073e−12 7.567548e−13 2.824684e−12 2.636674e−12 C3 −2.550937e−17 8.072280e−16 −8.040857e−16 −3.870631e−15 7.268545e−16 C4 −2.008613e−19 −1.589989e−19 −2.373612e−20 −2.969833e−19 −1.576215e−19 C5 6.058069e−23 3.137776e−23 1.268368e−23 6.242046e−22 1.095770e−22 C6 −9.717788e−27 −5.193051e−27 −3.735037e−27 −7.218140e−26 −3.106810e−26 C7 8.441816e−31 3.741282e−31 2.516910e−31 −5.174396e−29 4.585559e−30 C8 −3.120207e−35 −1.034688e−35 −8.393442e−36 1.110006e−32 −3.071967e−34 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 21 23 24 27 28 K 0 −3.141 −1.33118 0 0 C1 −2.862443e−08 −2.174149e−08 1.549149e−08 8.131862e−08 7.955643e−08 C2 −8.771349e−13 2.517297e−13 3.397419e−14 −1.707739e−12 2.867120e−12 C3 −1.596517e−17 −5.825790e−18 1.032630e−19 −3.301596e−17 −1.099153e−15 C4 −4.646004e−21 1.362810e−22 1.136332e−22 −5.761262e−20 3.424317e−20 C5 8.126190e−25 −3.290251e−27 −8.250734e−27 4.724568e−24 3.332299e−25 C6 −1.135755e−28 6.790431e−32 3.149468e−31 −1.202012e−28 −4.827974e−29 C7 7.299024e−33 −9.159117e−37 −5.928263e−36 4.082908e−34 2.861844e−33 C8 −2.111452e−37 6.183391e−42 4.153068e−41 1.760434e−38 −6.298301e−38 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 31 32 35 36 38 K 0 0 0 0 0 C1 −8.939854e−08 −1.036340e−07 −9.696640e−08 8.511140e−08 −6.457556e−08 C2 4.348686e−12 1.316189e−12 1.108503e−13 −2.457731e−12 8.723554e−13 C3 −8.114178e−16 6.095759e−17 −1.060162e−16 3.903750e−17 −3.888178e−17 C4 6.060580e−20 2.984406e−21 8.228345e−21 −6.588883e−21 6.708466e−22 C5 −3.926918e−24 5.719431e−26 −4.559678e−25 5.019357e−25 −3.249478e−26 C6 7.618517e−29 2.198926e−29 1.569417e−29 −1.721031e−29 3.981782e−30 C7 8.937963e−33 −2.899121e−33 −4.855487e−34 2.943619e−34 −1.652000e−34 C8 −7.773344e−37 7.179029e−38 4.866053e−39 −4.420955e−39 1.394293e−39 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 40 45 47 49 K 0 0 0 0 C1 −3.047152e−08 2.876681e−08 −7.237631e−08 3.127564e−08 C2 −2.503917e−13 −4.981655e−13 7.328144e−12 −1.483849e−12 C3 −2.036991e−17 2.984706e−17 −5.046596e−16 2.815259e−17 C4 2.564810e−21 −7.422489e−22 1.891226e−20 2.747470e−20 C5 −1.078825e−25 1.333563e−26 −2.625122e−25 −3.683041e−24 C6 2.525531e−30 −4.886557e−31 5.993731e−30 2.331163e−28 C7 6.070121e−36 5.284852e−36 −6.235738e−34 −8.136306e−33 C8 −9.848310e−40 3.056734e−41 1.667827e−38 1.346431e−37 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00

TABLE 11 NA = 1.43; field size 26 mm * 4 mm; λ = 193 nm Surface Radius Thickness Material Index (193 nm) ½ Diameter  0 0.000000 33.332248 AIR 1.00000000 60.000  1 0.000000 −0.004263 AIR 1.00000000 72.779  2 357357.144810 AS 46.089360 SIO2V 1.56078570 76.013  3 −417.562806 74.837927 AIR 1.00000000 81.763  4 280.404005 60.022974 SIO2V 1.56078570 101.278  5 −166.627712 AS 0.999622 AIR 1.00000000 101.071  6 116.529317 38.169032 SIO2V 1.56078570 71.306  7 405.500190 15.365869 AIR 1.00000000 60.252  8 −238.458946 9.999795 SIO2V 1.56078570 56.004  9 211.906189 AS 10.592661 AIR 1.00000000 47.114 10 0.000000 0.000000 AIR 1.00000000 46.365 11 0.000000 2.965376 AIR 1.00000000 46.365 12 0.000000 9.999570 SIO2V 1.56078570 48.729 13 0.000000 0.999095 AIR 1.00000000 53.095 14 251.808655 75.306859 SIO2V 1.56078570 59.619 15 −209.119448 AS 19.949752 AIR 1.00000000 76.307 16 297.229724 41.623543 SIO2V 1.56078570 91.301 17 −368.032393 AS 17.309640 AIR 1.00000000 91.926 18 −304.574570 9.998928 SIO2V 1.56078570 86.542 19 −1835.490188 AS 37.493067 AIR 1.00000000 85.640 20 0.000000 269.847723 AIR 1.00000000 88.712 21 −193.435450 AS — REFL 1.00000000 156.793 22 230.296849 AS 269.847723 REFL 1.00000000 162.808 23 0.000000 37.496545 AIR 1.00000000 115.972 24 222.765081 32.374348 SIO2V 1.56078570 118.274 25 139.308788 AS 20.243523 AIR 1.00000000 111.594 26 504.166848 AS 50.121407 SIO2V 1.56078570 111.843 27 −296.072806 9.056420 AIR 1.00000000 110.445 28 −602.578656 9.999975 SIO2V 1.56078570 97.132 29 93.726568 AS 13.818669 AIR 1.00000000 83.497 30 110.971133 AS 9.999545 SIO2V 1.56078570 83.171 31 124.632154 62.097682 AIR 1.00000000 80.656 32 −132.174351 11.899629 SIO2V 1.56078570 81.715 33 −40607.350265 AS 24.348045 AIR 1.00000000 102.447 34 1799.174156 AS 51.395108 SIO2V 1.56078570 115.369 35 −187.360985 0.997962 AIR 1.00000000 123.742 36 −700.986626 AS 65.447368 SIO2V 1.56078570 144.945 37 −188.074155 1.059137 AIR 1.00000000 150.242 38 −5408.105536 AS 29.786331 SIO2V 1.56078570 175.144 39 −1608.220868 35.803900 AIR 1.00000000 175.488 40 202.569243 79.929030 SIO2V 1.56078570 175.217 41 −580676.026640 AS 28.659957 AIR 1.00000000 170.624 42 0.000000 0.000000 AIR 1.00000000 171.264 43 0.000000 −25.369612 AIR 1.00000000 171.264 44 192.367691 75.692630 SIO2V 1.56078570 153.859 45 784.958025 AS 0.995706 AIR 1.00000000 148.467 46 127.716618 51.629289 SIO2V 1.56078570 104.469 47 697.612041 AS 0.960830 AIR 1.00000000 94.717 48 50.984791 43.213390 SIO2V 1.56078570 47.246 49 0.000000 3.444444 HINDLIQ 1.65002317 21.011 50 0.000000 0.000000 15.000

TABLE 11A Aspheric constants SRF 2 5 9 15 17 K 0 0 0 0 0 C1 −6.886423e−08 −5.399934e−09 7.670365e−07 −1.468962e−08 2.941498e−08 C2 5.485090e−13 −1.665701e−13 −1.648448e−11 1.288281e−11 −2.652838e−11 C3 −1.310182e−15 1.141289e−15 −7.138563e−14 1.151797e−16 8.340750e−16 C4 4.553614e−19 −2.207616e−19 2.971898e−17 −1.481358e−19 8.678296e−20 C5 −1.343018e−22 2.537949e−23 −1.082266e−20 2.848823e−23 1.861559e−23 C6 1.960673e−26 −1.868665e−27 5.685298e−24 −7.123479e−27 −4.697518e−27 C7 −1.250480e−30 8.263513e−32 −2.060132e−27 9.661060e−31 3.445831e−31 C8 1.179973e−35 −1.667241e−36 2.897054e−31 −4.638795e−35 −8.934923e−36 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 19 21 22 25 26 K 0 −1.49741 −1.62646 0 0 C1 2.476984e−08 −1.522752e−08 1.471219e−08 −2.496187e−07 −1.110036e−07 C2 1.500487e−11 −1.396376e−15 3.623941e−14 9.991017e−12 2.261667e−11 C3 −4.386995e−16 −1.165187e−18 −1.591633e−18 6.981563e−16 1.059597e−16 C4 4.006150e−20 5.254699e−23 2.344572e−22 −5.968529e−20 −2.875234e−19 C5 −2.400161e−23 −2.875966e−27 −1.338490e−26 4.601373e−24 4.467403e−23 C6 2.853406e−27 8.782897e−32 4.654398e−31 −1.413493e−27 −4.303454e−27 C7 −1.087783e−31 −1.455581e−36 −8.796362e−36 1.323528e−31 2.330243e−31 C8 4.311181e−37 9.964499e−42 7.028833e−41 −3.872736e−36 −5.208998e−36 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 29 30 33 34 36 K 0 0 0 0 0 C1 −2.267301e−07 −8.519491e−08 2.440652e−07 1.018655e−07 −3.263771e−08 C2 −1.583065e−11 −3.972995e−11 −2.702153e−11 −2.093056e−11 4.414943e−12 C3 6.128819e−15 4.407665e−15 3.482308e−16 1.840200e−15 −3.226771e−16 C4 −1.569530e−18 −6.334167e−19 2.746742e−19 −1.201814e−19 1.696874e−20 C5 1.407627e−22 −1.585820e−23 −4.143028e−23 5.796403e−24 −7.791980e−25 C6 −7.921382e−27 1.683303e−26 3.274508e−27 −1.854295e−28 2.511951e−29 C7 −3.596221e−31 −2.727972e−30 −1.458485e−31 3.605510e−33 −4.563870e−34 C8 5.039527e−35 1.787510e−34 3.028396e−36 −4.430267e−38 3.025968e−39 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 38 41 45 47 K 0 0 0 0 C1 9.235685e−09 2.984374e−08 −5.662983e−08 4.426415e−08 C2 −4.548242e−13 3.795044e−13 5.304155e−12 −1.939003e−13 C3 4.711657e−17 2.322935e−17 −2.666811e−16 4.722428e−16 C4 −6.285778e−22 −2.741671e−21 7.087400e−21 −3.883053e−20 C5 −3.584554e−26 1.065528e−25 −2.346928e−26 −4.947922e−25 C6 1.500601e−30 −1.995489e−30 −3.324754e−30 4.961940e−28 C7 −2.277407e−35 1.285834e−35 7.276997e−35 −4.556416e−32 C8 1.311951e−40 2.890527e−41 −3.730749e−40 1.483979e−36 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00

TABLE 15 NA = 1.50; field size 26 mm * 5 mm; λ = 193 nm Surface Radius Thickness Material Index (193 nm) ½ Diameter  0 0.000000 56.505360 AIR 1.00000000 61.600  1 0.000000 0.628593 AIR 1.00000000 84.411  2 0.000000 9.999465 SIO2V 1.56078570 84.665  3 0.000000 1.018383 AIR 1.00000000 87.136  4 267.687560 23.051668 SIO2V 1.56078570 94.506  5 2076.339784 3.011269 AIR 1.00000000 95.214  6 195.468828 118.243767 SIO2V 1.56078570 99.907  7 213.465552 65.301393 AIR 1.00000000 87.739  8 233.154018 24.923341 SIO2V 1.56078570 92.865  9 −1992.179958 AS 1.169743 AIR 1.00000000 91.232 10 397.921478 69.915906 SIO2V 1.56078570 91.709 11 505.661172 17.194249 AIR 1.00000000 95.812 12 −735.689494 9.999732 SIO2V 1.56078570 96.173 13 887.983169 8.242783 AIR 1.00000000 100.163 14 0.000000 0.000000 AIR 1.00000000 101.571 15 0.000000 42.782393 AIR 1.00000000 101.571 16 −410.552179 AS 78.848881 SIO2V 1.56078570 128.012 17 −163.270786 336.654237 AIR 1.00000000 134.938 18 237.665945 66.291266 SIO2V 1.56078570 153.690 19 −1317.124240 AS 86.415659 AIR 1.00000000 152.243 20 222.206724 27.565105 SIO2V 1.56078570 112.997 21 921.104852 AS 68.984477 AIR 1.00000000 110.393 22 0.000000 0.000000 AIR 1.00000000 82.262 23 0.000000 −223.984401 REFL 1.00000000 82.262 24 112.393927 AS −9.995120 SIO2V 1.56078570 93.383 25 618.177768 −30.194887 AIR 1.00000000 110.198 26 180.843143 −9.993434 SIO2V 1.56078570 111.320 27 459.728303 −49.418013 AIR 1.00000000 131.268 28 166.364160 49.418013 REFL 1.00000000 133.173 29 459.728303 9.993434 SIO2V 1.56078570 130.248 30 180.843143 30.194887 AIR 1.00000000 106.184 31 618.177768 9.995120 SIO2V 1.56078570 102.211 32 112.393927 AS 223.984401 AIR 1.00000000 87.128 33 0.000000 0.000000 AIR 1.00000000 69.972 34 0.000000 −63.976352 REFL 1.00000000 69.972 35 412.103957 −20.679211 SIO2V 1.56078570 92.437 36 203.153828 −0.998595 AIR 1.00000000 95.263 37 −1996.505583 −25.026685 SIO2V 1.56078570 104.114 38 387.517974 −0.999117 AIR 1.00000000 105.544 39 −217.409028 −35.834400 SIO2V 1.56078570 112.665 40 −1732.046627 −89.753105 AIR 1.00000000 111.738 41 −432.227186 −24.454670 SIO2V 1.56078570 100.002 42 −429.393785 AS −61.820584 AIR 1.00000000 96.269 43 127.267221 AS −9.998963 SIO2V 1.56078570 96.639 44 −354.132669 −7.868044 AIR 1.00000000 110.880 45 −523.720649 −14.975470 SIO2V 1.56078570 112.701 46 −341.520890 AS −0.997791 AIR 1.00000000 118.281 47 −411.353502 −48.777625 SIO2V 1.56078570 120.957 48 342.083102 −8.810353 AIR 1.00000000 122.794 49 514.961229 AS −14.987375 SIO2V 1.56078570 123.090 50 291.403757 −79.216652 AIR 1.00000000 128.222 51 826.480933 AS −24.931069 SIO2V 1.56078570 151.976 52 388.289534 −1.073107 AIR 1.00000000 155.772 53 1460.275628 −24.262791 SIO2V 1.56078570 162.233 54 543.277065 −0.999651 AIR 1.00000000 163.887 55 −4320.460965 −27.112870 SIO2V 1.56078570 168.245 56 901.554468 −0.999423 AIR 1.00000000 168.871 57 −227.624376 −78.149238 SIO2V 1.56078570 170.522 58 −2243.544699 −9.897025 AIR 1.00000000 167.855 59 0.000000 0.000000 AIR 1.00000000 165.919 60 0.000000 −43.822974 AIR 1.00000000 165.919 61 −193.437748 −56.826827 SIO2V 1.56078570 128.975 62 4852.914186 AS −1.258966 AIR 1.00000000 124.642 63 −126.542916 −25.022273 SIO2V 1.56078570 89.797 64 −202.284936 AS −0.996510 AIR 1.00000000 78.587 65 −95.520347 −72.724717 LUAG 2.10000000 70.909 66 0.000000 −6.000000 HIINDLIQ 1.64000000 28.915 67 0.000000 0.000000 15.401

TABLE 15A Aspheric constants SRF 9 16 19 21 24 K 0 0 0 0 0 C1 1.993155e−07 7.648792e−08 1.310449e−08 1.499407e−08 −1.140413e−07 C2 −2.965837e−11 −1.147476e−12 −1.473288e−13 4.898569e−13 −1.405657e−12 C3 7.084938e−15 −1.620016e−16 1.789597e−18 −4.831673e−18 −6.422308e−16 C4 −1.108567e−18 1.291519e−20 −3.347563e−23 5.603761e−22 9.595133e−20 C5 1.294384e−22 −4.536509e−25 7.855804e−28 1.107164e−28 −1.651690e−23 C6 −8.666805e−27 8.063130e−30 −1.561895e−32 −1.720748e−31 1.285598e−27 C7 2.821071e−31 −5.992411e−35 1.565488e−37 3.402783e−35 −5.054656e−32 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 32 42 43 46 49 K 0 0 0 0 0 C1 −1.140413e−07 −4.189168e−08 −1.685701e−07 6.336319e−09 5.280703e−08 C2 −1.405657e−12 −3.147936e−13 9.635698e−12 4.071242e−12 1.157060e−12 C3 −6.422308e−16 −1.294082e−18 −1.217963e−15 −3.577670e−16 −7.824880e−17 C4 9.595133e−20 −2.828644e−22 1.012583e−19 2.732048e−20 7.171704e−21 C5 −1.651690e−23 4.489648e−26 −8.858422e−24 −1.655966e−24 −3.888551e−26 C6 1.285598e−27 −1.468171e−29 4.866371e−28 6.535740e−29 −2.007284e−29 C7 −5.054656e−32 1.147294e−33 −1.337836e−32 −1.353076e−33 4.237726e−34 C8 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 C9 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 SRF 51 62 64 K 0 0 0 C1 −6.339317e−09 4.857833e−08 −2.139384e−07 C2 9.839286e−13 −8.830803e−12 1.525695e−11 C3 −3.557535e−17 7.521403e−16 −4.799207e−15 C4 2.050828e−21 −4.932093e−20 1.286852e−18 C5 −7.703006e−26 2.223792e−24 −3.670356e−22 C6 2.045013e−30 −5.700404e−29 7.133596e−26 C7 −2.770838e−35 −3.566708e−35 −9.239454e−30 C8 0.000000e+00 4.807714e−38 6.969720e−34 C9 0.000000e+00 −1.056980e−42 −2.499170e−38 

1.-20. (canceled)
 21. A projection objective, comprising: a plurality of optical elements configured so that, during use of the projection objective, radiation follows a path through the projection objective to image an object field in an object surface onto an image field in an image surface, the optical elements defining: a first group of refractive optical elements; a second group of optical elements downstream of the first group of refractive optical elements along the path, the second group of optical elements comprising a concave mirror; and a third group of refractive optical elements downstream of the second group of optical elements along the path, wherein: the projection objective has a first pupil surface along the path; and the projection objective comprises a Fourier lens group comprising a negative lens group arranged so that an absolute value of a Petzval radius at the first pupil surface is greater than 150 mm.
 22. The projection objective of claim 21, wherein the negative lens in the Fourier lens group is arranged optically close to the first pupil surface.
 23. The projection objective of claim 21, wherein the negative lens in the Fourier lens group is in the first group of refractive optical elements.
 24. The projection objective of claim 23, wherein the first pupil surface is in the first group of refractive optical elements along the path.
 25. The projection objective of claim 21, wherein the third group of refractive optical elements comprises an aperture stop, and the projection objective comprises at most three lenses between the aperture stop and the image surface along the path.
 26. The projection objective of claim 25, further comprising first and second folding mirrors, wherein the first folding mirror is upstream of the concave mirror along the path, and the second folding mirror is downstream of the concave mirror along the path.
 27. The projection objective of claim 26, wherein the second group of optical elements includes only one concave mirror.
 28. The projection objective of claim 25, wherein the projection objective is a folded projection objective.
 29. The projection objective of claim 25, wherein the projection objective has a second pupil surface, and the concave mirror is in the region of the second pupil surface.
 30. The projection objective of claim 25, wherein an optical axis of the first group of refractive optical elements is parallel to an optical axis of the third group of refractive optical elements, and an optical axis of the second group of optical elements is not parallel to the optical axis of the first group of refractive optical elements.
 31. The projection objective of claim 25, wherein the object field is entirely outside an optical axis of the projection objective, and the image field is entirely outside the optical axis of the projection objective.
 32. The projection objective of claim 21, further comprising first and second folding mirrors, wherein the first folding mirror is upstream of the concave mirror along the path, and the second folding mirror is downstream of the concave mirror along the path.
 33. The projection objective of claim 32, wherein the second group of optical elements includes only one concave mirror.
 34. The projection objective of claim 21, wherein the second group of optical elements includes only one concave mirror.
 35. The projection objective of claim 21, wherein the projection objective is a folded projection objective.
 36. The projection objective of claim 21, wherein the projection objective has a second pupil surface, and the concave mirror is in the region of the second pupil surface.
 37. The projection objective of claim 21, wherein an optical axis of the first group of refractive optical elements is parallel to an optical axis of the third group of refractive optical elements, and an optical axis of the second group of optical element is not parallel to the optical axis of the first group of refractive optical elements.
 38. The projection objective of claim 21, wherein the object field is entirely outside an optical axis of the projection objective, and the image field is entirely outside the optical axis of the projection objective.
 39. The projection objective of claim 21, wherein the first group of refractive optical elements defines a first refractive objective part configured to generate a first intermediate image from radiation coming from the object surface, and the first, refractive objective part includes the first pupil surface.
 40. The projection objective of claim 39, wherein the concave mirror is configured to image the first intermediate image into a second intermediate image, and the second group of optical elements defines a second objective part which includes a second pupil surface optically conjugated to the first pupil surface.
 41. The projection objective of claim 40, wherein the group of optical elements defines a third objective part which is configured to image the second intermediate image onto the image surface, and the third objective part includes a third pupil surface optically conjugated to the first and second pupil surfaces.
 42. The projection objective of claim 41, wherein the Fourier lens group is between the object surface and the first pupil surface along the path.
 43. The projection objective of claim 42, wherein the third objective part comprises an aperture stop, and the projection objective comprises at most three lenses between the aperture stop and the image surface along the path.
 44. A system, comprising: an illumination system; and a projection objective according to claim 21, wherein the system is a microlithography projection-exposure system. 